The crew of the Apollo 10 mission revealed that they heard a music-like noise on the far side of the moon in an episode of the Science Channel series “NASA’s Unexplained Files.” Astronauts Tom Stafford, John Young, and Eugene Cernan can be heard on recordings discussing about the whistling sound which lasted almost an hour, and whether to report it to NASA.

The recordings were sent to Mission Control to be transcribed, archived, and classified. Technicians say that the sound may have come from the interference from VHF (very high frequency) radios on the command module and lunar module interacting with one other.

“The Apollo 10 crew was very used to the kind of noise that they should be hearing. Logic tells me that if there was something recorded on there, then there was something there,” says Apollo 15 Command Module Pilot Al Worden. “NASA would withhold information from the public if they thought it was in the public’s best interest.

The Apollo 10 mission took place in May 1969 as a “dress rehearsal” for Apollo 11’s historic flight in July 1969. The crew entered the lunar orbit and got within 5,000 feet of the surface, which included the far side of the moon where spacecrafts lose contact with Earth.

“You don’t hear about anything like that until years after the incident occurs, and then you kind of wonder, because it’s such an old memory of those things that you get concerned about if they were making something up or was there something really there? Because you never really know,” Worden adds. “If you’re behind the moon and hear some weird noise on your radio, and you know you’re blocked from the Earth, then what could you possibly think?”

“We’d had a lot of incidents where guys who flew in space saw and heard things that they didn’t recognize, and you wonder about all of that. I have a very open mind about what could’ve happened. It’s somebody’s hearsay evidence — it’s only a visual or audio event, which is hard to pin down. Recollection is one thing, but actual proof is something entirely different,” Worden concludes.